1. Field of the Invention
The present invention relates to the management and conservation of irrigation water, primarily for, but not limited to, residential and commercial landscaping applications, and more specifically, to a greatly simplified method for doing so based upon seasonal temperature variations and geographic locations.
2. Description of the Prior Art
Many regions of the United States lack sufficient water resources to satisfy all of their competing agricultural, urban, commercial and environmental needs. The “California Water Plan Update, Bulletin 160-98,” published by the California Department of Water Resources using 1995 calendar year data, estimated that approximately 121.1 million acre feet (maf) of water is needed to satisfy the annual water needs of the State of California alone. Of this amount, approximately forty-six percent is required for environmental purposes, forty-three percent for agricultural purposes, and eleven percent (approximately 13.3 maf) for usage in urban areas. The Bulletin further estimated that California suffers a shortage of 1.6 maf during normal years, and 5.1 maf in drought years. These shortages are expected to increase steadily through the year 2020 due to expected significant increases in the state population.
At the Feb. 17, 2004, EPA-sponsored “Water Efficient Product Market Enhancement Program” in Phoenix, Ariz., for landscaping irrigation systems and controllers, it was projected that thirty-six states will have severe water shortages by the year 2010. A significant portion of this projected shortage was attributed to user neglect and irrigation controller inefficiency. The 2003 California census revealed that there were over twenty million single family residences and apartments within the state. The California Urban Water Conservation Council estimated that the average household utilized one-half acre foot of water (162,500 gallons) annually, and that fifty-five percent (89,375 gallons) of this amount was used for landscape irrigation. It further estimated that approximately one-third of the irrigation water was wasted, either due to inefficient irrigation systems or inadequate controller programming, oftentimes due in part to complicated controller programming procedures required of the operator. This results in a total annual waste of 1.81 maf of water for California households alone. Excessive water usages in municipal and commercial areas, golf courses and schools further contribute to the water shortage.
Such water shortages have forced many municipalities to enact strict water conservation measures. For its part, the agricultural industry has responded to this shortage by resorting to drip, micro and other low-volume irrigation systems. Urban communities have imposed strict irrigation schedules, and required the installation of water meters and auditors to enforce those schedules. Commercial and environmental users have enacted similar measures. However, there is no consensus among these various consumers as to the most effective water conservation method or automated control system.
Residential and commercial irrigation consumers are responsible for a significant percentage of wasted water. A report entitled “Water Efficient Landscaping” by the United States Environmental Protection Agency (EPA), dated September 2002, publication number EPA832-F-02-002, states the following: “[a]ccording to the U.S. Geological Survey, of the 26 billion gallons of water consumed daily in the United States (Amy Vickers, 2002 “Handbook of Water Use and Conservation”), approximately 7.8 billion gallons, or 30% is devoted to outdoor uses. The majority of this is used for landscaping”
A significant reason for this over-utilization of landscape water was revealed in a marketing study conducted by the Irrigation Association (IA) and presented at the 2003 IA “Smart Water Application Technology” conference in San Diego, Calif. The study indicated that most consumers typically adjust their irrigation schedule only two to five times per year, rather than on a daily or weekly basis, regardless of changes in environmental conditions. The relatively high cost of labor in many municipalities further prohibits frequent manual adjustments of irrigation controllers. This generally results in over-irrigation and runoff, particularly during the off-seasons, oftentimes by as much as one to two hundred percent. Furthermore, in municipalities that limit irrigation to certain days or intervals, the common practice is to over-water during the permitted watering periods in order to “carry over” until the next watering period. However, this practice is counter-productive, in that severe over-irrigation results in increased water run-off and evaporation.
Soil moisture sensing devices and other methods of water conservation, have been available for decades, but have enjoyed only limited success. Such devices and methods generally call for inserting moisture sensors into the soil to measure the soil moisture content. Newer soil moisture sensing technologies have more recently been developed, and claim to be theoretically accurate in measuring plant water needs. However, regardless of the level of technology, such devices and methods are often problematic due to the location and number of sensors necessary to obtain accurate soil moisture readings, the high costs of installing and maintaining the sensors, and the integrity and reliability of the sensors data.
Other irrigation controllers utilize meteorological data to estimate the evapotranspiration, or ET, for a particular region. This ET represents the amount of water needed by plants to replace water lost through plant absorption and evaporation, and is expressed in inches or millimeters of water per day. The United States Food and Agriculture Office (USFAO), in its Irrigation and Drainage Paper No. 24, entitled “Crop Water Requirements,” noted that “a large number of more or less empirical methods have been developed over the last fifty years by numerous scientists and specialists worldwide to estimate ET from different climatic variables.”
There are at least 15 different ET formulas. Each of these formulas provides a different result for the reference ET (ETo). In their paper entitled “Methods to Calculate Evapotranspiration: Differences and Choices,” Diego Cattaneo and Luke Upham performed a four-year comparison of four different ETo formulas—the Penman-Monteith formula, the Schwab formula, the Penman formula, and the Penman program. The comparison revealed that the results from the four recognized formulas sometimes varied by as much as seventy-five percent.
The Penman-Monteith formula is currently recommended as the “standard” by both the USFAO and California Irrigation Management Information System (CIMIS), with variances of less than twenty percent considered ideal. The Penman-Monteith formula is as follows:
  ETo  =                    Δ        ⁡                  (                      Rn            -            G                    )                            λ        [                  Δ          +                      Y            ⁡                          (                              1                +                                  CdU                  ⁢                                                                          ⁢                  2                                            )                                            +                  y        ⁢                                  ⁢                  37                      Ta            +            273.16                          ⁢        U        ⁢                                  ⁢        2        ⁢                  (                      Es            -            Ea                    )                            Δ        +                  Y          ⁡                      (                          1              +                              CdU                ⁢                                                                  ⁢                2                                      )                              
The variables within this formula represent the following:                ETo=grass reference evapotranspiration in millimeters per day.        Δ=slope of saturation vapor pressure curve kPa° C. at the mean air temperature.        Rn=net radiation (MJm−2h−1).        G=soil heat flux density (MJm−2h−1).        Y=psychrometric constant (kPa° C.).        Ta=mean hourly air temperature (° C.).        U2=wind speed at two meters (m s−1).        Es=saturation vapor pressure (kPa) at the mean hourly air temperature in ° C.        Ea=actual vapor pressure (kPa) at the mean hourly air temperature in ° C.        λ=latent heat of vaporization (MJkg−1).        Cd=bulk surface resistance and aerodynamics resistance coefficient.        
The simplest ET formula is the Hargreaves formula proposed by the College of Tropical Agriculture and Human Resources at the University of Hawaii at Manoa. Its equation is described in the College's Fact Sheet Engineer's Notebook No. 106, published May 1997, in an article entitled “[a] Simple Evapotranspiration Model for Hawaii,” as follows:ETo=0.0135(T+17.18)Rs 
The variables within this formula represent the following:                ETo=potential daily evapotranspiration in mm/day.        T=mean daily temperature (° C.).        Rs=incident solar radiation converted to millimeters of water per day (MJ).This formula is theoretical and, to the inventor's knowledge, untested. Furthermore, it relies upon the same ET theories and interrelationships as the other formulas disclosed above. As described herein, such reliance causes the Hargreaves formula to possess the same shortcomings as the other ET formulas.        
A number of irrigation controller manufacturers offer “smart” (self-adjusting) irrigation controllers. Such controllers generally incorporate some form of ET. Several of them obtain the environmental data to calculate ET from historical records, while others utilize adjacently located weather stations to obtain real-time data. Others receive such information from a network of existing weather stations by radio, satellite or pager means.
The following U.S. patents all disclose various methods by which an irrigation controller calculates or adjusts an irrigation schedule based upon historical, distal, or local ETo: U.S. Pat. Nos. 4,962,522; 5,208,855; 5,479,339; 5,696,671; and 6,298,285. All of these methods calculate ETo values or receive them from external sources, and use such values to adjust and regulate irrigation. Such external sources may be CIMIS ET databases, local sensors, cable lines or broadcast stations. Several of these methods also utilize other data, such as precipitation.
Unfortunately, methods incorporating ET formulas, and the installation, comprehension and programming of controllers utilizing such methods, including those cited in the referenced patents above, are far too complex for the average user to understand and implement. Such a conclusion was reached in a recent study of ET controllers by the Irvine Ranch Water District, entitled “Residential Weather Based Irrigation Scheduling Study.” The study stated the following: “The water agency solution to date has been to conduct residential audits, leaving the homeowner with a suggested watering schedule, hoping it would then be followed. These programs have had limited effect and a short-term impact. A preferred solution would be to install irrigation controllers that automatically adjust watering times based on local weather conditions. Unfortunately, until now, these large landscape control systems have been far too complex and expensive for residential applications.”
Such complexity is underscored by the one hundred forty-five principal symbols and acronyms identified by the USFAO for use and description of the factors and variables related to ET theory and its various formulas, covering such variables as: the capillary rise; the resistance correction factor; the soil heat capacity; the psychrometer coefficient; and the bulk stomatal resistance of a well-illuminated leaf. The sheer number of variables renders ET theory difficult to explain, understand and apply, especially for an unsophisticated consumer with little or no scientific or meteorological background. For example, the manual for one ET-based controller currently on the market comprises over one hundred fifty pages of instructions and explanations. Such unfamiliarity and complexity increase the margins of error already associated with the various ET formulas, further diminishing their effectiveness.
Water districts, irrigation consultants, manufacturers, the Irrigation Association, the Center for Irrigation Technology and other attendees at the EPA's Water Efficient Product Market Enhancement Program estimated that, due to the complexity, cost, impracticality of installation and difficulty in programming current irrigation controllers, less than one percent of all commercial and residential landscape irrigation systems currently and effectively utilize some form of the ET or moisture sensing method. Such scattered adoption exists despite over fifty years of ET research, and over thirty years of ground moisture sensing technology. The magnitude of such ineffectiveness is underscored by the fact that there are over two million new controllers installed annually in the United States alone, and over fifty million controllers in use today. Even if the ET or ground moisture sensing methods provided one hundred percent efficiency, which they do not, the limited adoption of these methods renders them an ineffective means of significant water conservation, since only one percent of the runoff and water waste would be prevented under perfectly-efficient conditions.
A second shortcoming of the ET method is its dependence upon numerous categories of local, real-time meteorological data. As indicated above, many variables must be measured in order to calculate ET. Data for each variable must be obtained by separate sensors, each one installed in a particular location. Such particularity requires an understanding of local environmental conditions and meteorology. Furthermore, accuracy requires that the data be received from local sensors—given the numerous microclimates existing within any one geographical area, data received from remotely located sensors may be inaccurate. The data must also be received and processed in real-time, since average or historical ET data may be inaccurate during periods of unusual or excessive heat, cold, or rain, or other deviations from historical climate patterns. Any inaccurate data would result in even greater ET deviations and inefficient irrigation.
ET measuring devices are generally also expensive to install and maintain. Sensors or weather stations must be placed within each microclimate to measure the different variables utilized by the formula of choice. Each weather station may cost up to several thousand dollars. Furthermore, all of these sensors or stations must undergo regular inspection, maintenance and calibration to insure that they continue to provide accurate data. This further increases the actual cost of each station. The sensors and stations must also be powered in some manner—depending upon the particular geographic location, AC power may not be readily available. All of these considerations increase the cost of implementing an ET-based irrigation system to a prohibitive level, and limit the widespread adoption of this method. Finally, all of this assumes that the weather station or sensors is even installable in a particular area—some areas, such as street medians or parks, are not suitable for weather station or sensor installation due to aesthetic reasons or the likelihood of vandalism.
Another shortcoming of ET-based controllers is that all of the ETo formulas (including the Hargreaves formula) are generally expressed in hundredths of an inch, or millimeters, of water per day. Thus, ETo must be converted to an actual irrigation time of minutes. Such a conversion is dependent upon the characteristics of the particular hydraulic system, such as the valve sizes, water flow rates, and sprinkler or drip irrigation precipitation rates. One conversion formula, proposed by the Austin (Texas) Lawn Sprinkler Association, calculates the sprinkler run time in minutes (T) as follows:
  T  =            60      ×      ETo      ×      Kc              Pr      ×      Ea      
The variables within this equation represent the following:                ETo=reference evapotranspiration rate, in inches.        Kc=the percentage crop coefficient.        Pr=the sprinkler precipitation rate, in inches per hour.        Ea=the percentage application efficiency of the hydraulics system.As an example of such complexity, the crop coefficient (Kc) is different for each crop or landscape plant or grass type. Determining the precipitation rate (Pr) requires knowledge of the hydraulic system specifications—the particular types of valves and sprinklers, the number of valves and sprinklers within the system, the water flow rate and operating pressure. Such information is not readily available to the average consumer. Instead, the consumer must expend additional time and money to retain an irrigation expert to configure and install the system.        
Another ET-to-irrigation-time conversion method, the ‘deficit irrigation practice,’ was proposed by the IA Water Management Committee in Appendix G of its October 2002 article entitled “Turf and Landscape Irrigation Best Management Practices.” Such conversion method comprised of ten separate formulas, and utilized a total of twenty-nine variables and constants, not including those utilized in calculating the ET value. Many of these variables represented concepts and relationships difficult for the average irrigation designer, much less a consumer, to understand, such as: the local landscape coefficient for the particular vegetation; available water depending upon the particular soil composition; allowable water depletion rate from the root zone; maximum percentage allowable depletion without plant stress; the water management factor necessary to overcome water management inefficiency; the whole day stress-based irrigation interval; water flow rates for the particular system; and, of course, ET.
Due to the urgency arising from severe national drought and environmental conditions, and the shortcomings of the various present technologies, the irrigation industry is currently researching alternative methods for water conservation and prevention of unattended runoff. The Center for Irrigation Technology in Fresno, Calif., along with other educational and research institutions and water conservation agencies, is conducting studies to determine the most effective water conservation method. On the national level, the EPA is considering the introduction of a “WaterStar” irrigation efficiency rating program similar to the “EnergyStar” rating system currently in use for equipment energy efficiency. The purpose of such an irrigation efficiency rating program is to promote consumer awareness and compliance as an alternative to mandated water conservation measures which would severely and negatively impact the irrigation industry, landscape aesthetics and the ecology.
It is clear from the foregoing discussion that the irrigation water management industry, in view of a politically and economically sensitive, and urgent, water crisis, is pursuing highly scientific, mathematical and/or technical approaches for resolving the problems of wasted irrigation water and drought conditions. Unsurprisingly, such approaches have met with limited success. The EPA, United States Department of Energy (DOE), ecologists, environmentalists, municipalities, water agencies, and research institutions are all searching for new methods that provide practical (as opposed to theoretical) irrigation efficiency—methods that overcome the particular shortcomings of the prior art.
Landscape water conservation also provides additional benefits. As noted by the EPA in its “Water Efficient Landscaping” guidelines, landscape water conservation also results in “decreased energy use (and air pollution associated with its generation) because less pumping and treatment of water is required and reduced runoff of storm water and irrigation water that carries top soils, fertilizers, and pesticides into lakes, rivers, and streams, fewer yard trimmings, reduced landscaping labor and maintenance costs, and extended life for water resources infrastructures (e.g. reservoirs, treatment plants, groundwater aquifers), thus reduced taxpayer costs.” Thus, there is an urgent need for irrigation systems that conserve water and energy, and minimize negative impact upon the environment, by automatically adjusting their schedules periodically in response to meteorological and seasonal changes.
The problem of irrigation mismanagement, and the main hurdle faced by these entities, can be simply summarized as follows: once a system is properly designed, most of the wasted landscape irrigation water and runoff is caused by not adjusting for daily, periodic, or seasonal changes. Such inaction is usually caused by the complexity and difficulty of determining the particular adjustment amounts. With that in mind, a correspondingly simple intuitive solution would be highly preferred over the existing highly theoretical and technical, but impractical, state of the art in moisture sensing and ET-based control systems.
It is therefore desirable to provide a simple, user-intuitive, and therefore readily accepted water conservation approach, particularly for a clearly understood automated method of calculating and implementing irrigation schedules. It is further desirable to provide a method that does not necessarily rely upon ground or air moisture sensing means, weather stations, or ET (either directly, or as a basis for deriving the sprinkler operating times). It is further desirable to provide a method that minimizes the margins and sources of errors by minimizing the number of sensor inputs required by the variables in the formula. It is further desirable to provide a method that utilizes minimal local, real-time meteorological data. It is further desirable that such a method be cost-efficient, affordable and usable by a large number of people and entities within the different industries. It is further desirable that such a method be understandable by the average consumer. It is further desirable that such a method be accomplished automatically, without requiring regular manual adjustments by the operator of the irrigation watering time settings or schedules.